Conventional cancer treatments involve a combination of chemotherapy, surgery, hormonal therapy and/or radiation treatment to eradicate neoplastic cells in a patient. Cancer chemotherapy is based on the use of drugs which kill replicating cells, hopefully faster than the agents kill the patient's normal cells. Surgery is used to reduce tumor bulk, but has little impact once the cancer has metastasized. Radiation is effective only in a localized area. All of these approaches pose significant drawbacks and added risks such as increased susceptibility to infection.
A further approach to cancer therapy is to target the immune system (“immunotherapy”) rather than or in addition to targeting the tumor itself.
However, despite advances in detection and treatment, many therapeutic protocols make only a minor contribution to survival rates, raising into question the cost-effectiveness and impact on quality of life of such treatments.
Recently, the important contribution of the innate and adaptive immune systems to the antitumour effects of conventional chemotherapy-based and radiotherapy-based cancer treatments has been described (Kroemer et al., 2013; Zitvogel et al., 2008).
It is now well established that gut commensal bacteria profoundly shape mammalian immunity (Hooper et al., 20112). Intestinal dysbiosis, which constitutes a disequilibrium in the bacterial ecosystem, can lead to overrepresentation of some bacteria able to promote colon carcinogenesis by favoring chronic inflammation or local immunosuppression (Grivennikov et al., 2012; Wu et al., 2009). However, the effects of microbial dysbiosis on non-gastrointestinal cancers are unknown.
Anticancer chemotherapeutics often cause mucositis (a debilitating mucosal barrier injury associated with bacterial translocation) and neutropenia, two complications that require treatment with antibiotics, which in turn can result in dysbiosis (Ubeda et al., 2010; van Vliet et al., 2010).
There is therefore a compelling need for the development of improved treatments for cancer which favor a constructive interaction, if not a synergy, between treatments such as chemotherapy and/or radiation and immunity.